Vehicle occupant weight detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of characterizing the occupant for purposes of determining whether to enable or disable deployment of the restraints. For example, it is generally desired to enable deployment for adult-weight occupants, and to disable deployment (or reduce deployment force) for child-weight occupants. In the case of infant or child seats (referred to herein collectively as child seats) that are placed on the vehicle seat and cinched down with a seat belt, it is generally believed that deployment should be disabled entirely. Unfortunately, there can be some ambiguity in the case of a child seat, particularly if the seat belt restraining the child seat is cinched very tightly, as a tightly cinched child seat can produce a weight reading similar to that of a small adult.
Accordingly, various attempts have been made to distinguish a child seat from other occupants producing a similar weight reading. In certain systems, for example, a special tag is affixed to the child seat for detection by a sensor located in the seat back or instrument panel. It has also been proposed to measure the seat belt restraining force to determine if a significant portion of the sensed weight is due to a cinched seat belt. However, both of these approaches are difficult to implement in an inexpensive and reliable manner.